How to permanently delete all traces of Kali Linux from Encypted Persistence USB?

I used a 64GB flash drive to boot Kali Linux from, to begin learning the OS. When the computer booted from the USB, I selected Encrypted Persistence Mode. After learning and messing around with the Terminal, I messed something up, and when I tried to re-format the USB, my 64GB capacity was only showing like 2GB. I have tried to research more about this, and got tutorials using dd, shred, etc. Which option would PERMANENTLY DELETE EVERYTHING on my USB, with no chance of recovering it back? My primary OS I use is Ubuntu 16.04, so I do have access to a Debian Terminal. From what I have researched people were also saying that overwriting the entire USB is the only way to do this, is that true? and if so, what are the steps to make this possible?